The invention relates to the control of thrust of the engines of aircraft. Modern aircraft, in particular transport airplanes, generally comprise a system for automatically controlling the thrust of the engines. Such a system is generally called auto-thrust system for the airplanes of the Airbus® range or auto-throttle system for the airplanes of the Boeing® range. When it is activated, such a system notably makes it possible to automatically control the thrust of the engines as a function of an aircraft speed setting. FIG. 1 illustrates an example of a standard system 20 for automatically controlling the thrust of the engines of an aircraft 1. This system comprises a processing unit 24, which corresponds, for example, to a processor of a flight control computer of the aircraft, such as, in particular, a computer of FG or FGC (Flight Guidance Computer) type. The automatic control of the thrust of the engines corresponds to a function implemented by software by the processing unit 24. The processing unit 24 is not specific to this function and it also implements other functions relating to the guiding of the aircraft. The processing unit 24 is configured to receive an aircraft speed setting VT, to determine a control setting for at least one engine of the aircraft as a function of the speed setting and to transmit a setting COM to a controller 30 of the at least one engine of the aircraft 1 as a function of the control setting. In order to implement a closed-loop control of the speed of the aircraft, the processing unit is further configured to receive a measurement of aircraft speed, for example an air speed VTAS. Usually, the controller 30 of the engine corresponds for example to a computer of FADEC (Full Authority Digital Engine Controller) type. FIG. 2 illustrates in more detail an example of function of the processing unit 24 corresponding to the automatic control of the thrust of the engines. A first adder S1 receives as input the speed setting VT and the air speed measurement VTAS and it produces as output a deviation between the speed setting VT and the air speed measurement VTAS. This deviation is multiplied by a first gain K12 by means of a first multiplier M1 whose output is linked to a first input of a second adder S2. Although not mandatorily, a second input of the second adder S2 receives the product, produced by means of a second multiplier M2, of an estimated value V of the derivative over time of the speed of the aircraft, by a second gain 2.K1.K2. This estimated value {dot over (V)} is supplied by an output of an estimator 26 which receives as input the air speed measurement VTAS. Although not mandatorily, the estimator 26 also receives, as input, a ground speed measurement VSOL. The second adder S2 produces, as output, a control setting for the engine corresponding to the derivative over time {dot over (T)} of the thrust of the engine. This derivative {dot over (T)} is received as input by an adapter 28 which converts it into a control setting for the engine corresponding to the derivative over time C{dot over (O)}M of a parameter COM accepted as input by the controller 30 of the engine. This derivative C{dot over (O)}M is received as input by an integrator 22 which supplies, as output, the engine control parameter COM and this parameter is supplied as input to the controller 30 of the engine. This engine control parameter 30 can correspond to any standard control parameter accepted by an aircraft engine controller, in particular an engine rotation speed N1 or N2, a percentage of a maximum engine thrust command, a power, etc. The two coefficients K1 and K2 used in the first gain and in the second gain make it possible to set the response time of the engine thrust control system 20 upon a change of the speed setting VT.
Such a system for automatically controlling the thrust of the engines is very efficient for controlling the air speed VTAS of the aircraft as a function of the speed setting VT, in nominal aircraft flight conditions. The responsiveness of the system is designed for these nominal flight conditions. In degraded flight conditions corresponding to the presence of turbulences, these turbulences can sometimes cause a momentary reduction of the speed of the aircraft. Since the response time of the system 20 is optimized for the nominal aircraft flight conditions, its responsiveness upon such a momentary reduction of the speed of the aircraft can seem too low for a pilot and the latter may feel it necessary to deactivate the automatic control system 20 to manually control the thrust of the engines.